The present invention relates to torsional vibration dampers used in vehicle drive-lines. Such dampers may comprise a twin mass flywheel or may be used in combination with a fluid coupling in a drive-line or may be used on their own in a drive-line.
Known twin mass flywheels include an input flywheel and an output flywheel which can rotate relative to each other to transmit power from an engine to a transmission and reduce torque fluctuations. Relative rotation of the flywheel masses is enabled by a bearing and the rotation is resisted by some form of damping means.
Examples of such devices are disclosed in granted patents GB 2229793, GB 2151332 and pending applications GB 2296072, W096/18832.
The axis of rotation of the engine power output shaft (engine crankshaft) is designed to rotate about an axis co-linear with the axis of rotation of the input shaft to the transmission. However under some working conditions the engine crankshaft can flex causing the input flywheel which is attached to the end of the crankshaft, to tip out of its nominal plane of rotation. The output flywheel which is attached to the input shaft to the transmission endeavours to rotate about its original axis in its nominal plane of rotation. This can cause the damping means which connects the input and output flywheels to become stressed and hence its working life is reduced. Furthermore this stressing can cause the bearing which allows the input and output flywheels to rotate relative to each other to have a reduced service life.
Similar problems can arise when the torsional vibration damper is used in combination with a fluid coupling as shown, for example, in earlier patent applications GB 2220464 and PCT/GB97/00362 where flexing of the engine crankshaft can cause the torsional vibration damper to be subjected to significant stresses which may reduce its service life.
It is an object of the present invention to provide a torsional vibration damper which at least partially mitigates the above problem.
Thus according to the present invention there is provided a torsional vibration damper comprising an input member designed to rotate generally in a first plane, an output member designed to rotate generally in a second plane, relative rotation of the input and output members being possible against the action of a damping means, the damper being characterised in that the first and second planes in which the input and output members rotate are able to tilt relative to each other during use of the damper.
The torsional vibration damper may be in the form of a twin mass flywheel in which the input and output members comprise input and output flywheel masses respective supported from each other for relative rotation via bearing means, the damper being characterised in that the bearing means is self-aligning to allow said tilting.
The torsional vibration damper may include bob weights which act to resist relative rotation of the input and output members, the bob weights being pivotally mounted on one member and having a connection with the other member. The pivotal mounting of the bob weights on said one member may be in the form of a self-aligning bearing.
The invention also provides a twin mass flywheel comprising a first and a second flywheel mass which can rotate relative to each other, the relative rotation being controlled by a damping means including a bob weight pivotally mounted on one flywheel mass and connected with the other flywheel mass, the flywheel being characterised in that the pivotal mounting on the one flywheel mass being in the form of a self-aligning bearing.
According to a further aspect of the invention there is provided a twin mass flywheel comprising a first and second flywheel mass which can rotate relative to each other, the relative rotation being controlled by damping means comprising a bob weight pivotally mounted on one flywheel mass and connected with the other flywheel mass by a link, one end of said link being pivotally connected to the bob weight and the other end of said link being pivotally connected to the other flywheel mass, the flywheel being characterized in that the pivotal connection of the link with the bob weight and/or the pivotal connection of the link with the other flywheel mass is in the form of a self-aligning bearing.
According to a further aspect of the present invention there is provided a torsional vibration damper comprising input and output members which can rotate relative to each other against the action of a damping means comprising at least one linkage arrangement, the or each linkage arrangement comprising a multi-link linkage having two or more circumferentially spaced main links pivotally mounted on one of the members with the or each circumferentially arranged pair of main links interconnected via a generally circumferentially extending connecting linkage pivotally connected at each end to respective main links, and an anchor link which pivotally connects the multi-link linkage with the other member, relative rotation of the input and output members causing the multi-link linkage to be pivoted relative to said one member by the anchor link, so that when the damper is rotating, relative rotation of the members is resisted by centripetal forces acting on the linkage arrangement, the damper being characterised in that at least one of the pivots of the multi-link linkage and/or anchor link being in the form of a self-aligning bearing.
The above torsional vibration damper may be in the form of a twin mass flywheel in which the input and output members comprise input and output flywheel masses respectively supported from each other for relative rotation via bearing means, the damper being characterised in that the bearing means is self-aligning.
The invention also provides a twin mass flywheel in which the bearing means which supports the flywheel masses for relative rotation has at least one of its inner or outer peripheries supported in a resilient support carried by the associated flywheel mass to allow said tilting.
The resilient support may comprise a resilient tolerance ring or a resilient plastics sleeve.
The tolerance ring may include generally radially extending projections which engage a groove or other formation in the associated bearing and/or a flange or other portion for attachment to the associated flywheel mass to locate the bearing axially relative to the associated flywheel mass.